Debris on the line at Aldgate East at 21:15 due to a bomb in the vicinity.[1]

At 22:16 a High Explosive bomb (designated 18/B in the drawing below) fractured the tunnels between Mornington Crescent and Euston on the Charing Cross branch of the Northern line. Water from broken mains entering the tunnel caused a power surge, tripping high-tension cables at Leicester Square, Belsize Park, and Golders Green. Failures at associated sub-stations also affected trolley bus services, and auto telephones north of Euston were disrupted. A gas main was also fracture, and the tunnels filled with debris. Services suspended between Strand [now Charing Cross] and Mornington Crescent.[1][2][3][4] See below for further details.

Suspected bomb on the track at Hounslow West at 21:12. Westbound services reversed at Hounslow Central until 21:30.[3]

Services suspended between Mansion House and Whitechapel at 21:45 due to debris on the track. Services resumed the following day.[3]

1. Edgware Road station 20/10 - no interference with services, but prevents use of lifts and esclators.[7]

Euston Station

At 15:00 on the 22nd, Lt-Col. AHL Mount, the Chief Inspecting Officer of Railways at the Ministry of Transport, visited the bomb site, and later reported:

"AT 10.10 p.m. on 21/10, one or more H.E. bombs (probably 500 kilo) fell and exploded in the centre of the street (wood blocks on concrete) at the junction of Eversholt Street and Phoenix Street (a continuation of Seymour Street) immediately outside the Eastern boundary of Euston Station and 100 yards [91 metres] south of the R.C.H. [Railway Clearing House] I understand that this was a deliberate dive bombing attack on Euston from just above the balloon barrage.

The crater was about 55 ft. [17 metres] diameter and 23 ft. [7 metres] deep, going down to the London Clay, the cover above the two 12 ft. 7 in. diameter tube running tunnels being about 44 ft. [13 metres] The roofs of both tunnels were broken in to an extent which it is impossible at present to estimate at points about 200 yards [183 metres] north of Euston Tube Station, and debris ran into both tunnels. (Iron of 12 ft. 7 in. diameter is not standard and therefore will have to be cast specially.)

Water mains of 16 in., 6 in., and 4 in. were fractured and before they could be closed (1½ hours?) water ran into the tunnels, flooded the suicide pits in the station and flowed southwards through the tunnel into the dip on the north side of Warren Street; but at no place were the tunnels flooded to a serious depth, and I understand that the station pumps (automatic) held the water, pending the provision of emergency pumping appliances."

Despite this extensive damage, Mount noted that things could have been even worse:

"A train on the south-bound road had just passed the point of damage when the explosion occurred, and windows in the rear part of the train were broken. Fortunately there were no casualties and refugees were cleared out of the station as a precautionary measure. Five trains were shut in between Euston and the river and will have to be worked back to Kennington by opening the floodgates. It is proposed, however, to retain one train in each tunnel in order to work a shuttle service between Euston and Strand."

Repairs were initially handled by civilian contractors, but shortage of workers meant that this work did not begin immediately, and when it did it was quickly handed over to half of 173rd Tunelling Company, Royal Engineers, under the command of a Captain Lander, on 5 November. Lander had previously worked as an engineer on the Underground, and by 13 November Mount was able to report:

"The Company had made good progress, 7 or 8 rings of a 7 ft. pilot tunnel having been erected in the one tunnel. The face had dried out considerably and appeared to be more consolidated than was anticipated. Captain Lander said that a flagstone or two had been met besides a quantity of tunnel iron.

In breaking away a piece of tunnel iron, the previous shift had cut a Post Office telephone cable which was located just outside the pilot iron. Post Office Engineers were making an examination at the same time, and were effecting repairs. Below the cable was one of the main secret Post Office telephone cables, which was also fouling the pilot iron. Another cable was apparently cut as a result of the accident."

Traffic resumed on 22 February 1941, after reconstruction of 34 rings of iron in one tunnel, and 41 rings in the other. On 28 February 1941 the civilian contractors (who remained responsible for the work being carried out by the Royal Engineers) sent Mount a piece of the bomb that had been uncovered during the repair work. Mount invited Wing Commander JCM Lowe of the Ministry of Home Security to examine the find, which he was able to on 5 March, making the judgement that it was a fragment from a 500 kilo device, but that the piece was so large that it suggested that the casing was weak due to poor manufacture, and it had fractured before detonation was fully complete.[5][8][9][1] Railway Executive Committee: Files: Form RWD1, 06:00-18:00 21/10/40, sheet 2 [Kew: National Archives, reference AN 2/1105][2] Ministry of Home Security, Key Points Intelligence Directorate: Reports and Papers, Daily Reports - October 1940: Damage Appreciation 21-22/10/40, page 2 [Kew: National Archives, reference HO 201/3][3] Railway Executive Committee: Files: Form RWD2, 18:00 21/10/40 to 06:00 22/10/40, sheet 1 [Kew: National Archives, reference AN 2/1105][4] Ministry of Home Security, Research and Experiments Department: Registered Papers: Damage to underground railways, drawing 14B [Kew: National Archives, reference HO 192/8][5] Ministry of Home Security, Research and Experiments Department: Notes: Notes on damage to railway tunnels by high explosive weapons Section 1, Tube railways. 26 March 1942. Author, Dr. EWJ Phillips [Kew: National Archives, reference HO 196/11][6] Ministry of Home Security, Key Points Intelligence Directorate: Reports and Papers, Daily Reports - October 1940: Railway Situation Report at 08:00 22/10/40, pages 1-2 [Kew: National Archives, reference HO 201/4][7] Ministry of Home Security, Key Points Intelligence Directorate: Reports and Papers, Daily Reports - October 1940: Railway Situation Report at 08:00 22/10/40, page 4 [Kew: National Archives, reference HO 201/4][8] Ministry of Transport and successors, Railway Divisions: Correspondence and Papers, Air Raid Damage - Underground Railways, 1940-1941 [Kew: National Archives, reference MT 6/2759][9] Ministry of Transport and successors, Railway Divisions: Correspondence and Papers, Air Raid Damage - Underground Railways, 1941-1942 [Kew: National Archives, reference MT 6/2766]